1. Field of the Invention
This invention relates to a signal compensator which automatically deletes noise components of signals approximated by sin .theta. and cos .theta., to produce sin .theta. and cos .theta. signals with low distortion. In particular, this invention can be applied to high-resolution measurement of position or angle for resolver and encoder signals through arc-tangent operation, to reduce measurement error.
2. Background Art
Resolvers and encoders are widely used to measure rotational angles (.theta.). Resolvers output one or more signal cycles approximated by sin .theta. and cos .theta. for each revolution, and these are processed (by arc-tangent operation) to produce a signal equivalent to .theta.. Encoders output several dozen to several thousand signal cycles approximated by sin .theta. and cos .theta. for each revolution, and in most cases the wave numbers of these signals are used to count the amount of rotation. Where higher resolution is required, arc-tangent operation is used to yield .theta. just as for resolvers.
To determine .theta. through arc-tangent operation with high precision, distortion-free sin .theta. and cos .theta. signals are essential. But, in fact, a variety of distortion components are included in the signals. Further, changes in temperature-related and time-related device characteristic can affect the amount of distortion present.
These problems can be avoided to some extent through the use of high-stability devices, temperature compensation for electronic circuitry, and precise adjustment. These measures, however, increase the cost of the equipment and still leave doubt as to reliability.
The inventor has proposed a magnetoresistance element (U.S. Pat. No. 4,843,365) providing low-distortion sin .theta. and cos .theta. signals through the use of a magnetic encoder. But even the use of this element can not prevent the obtained signal from degenerating through amplifier zero drift, gain fluctuation, and non-linearity. In addition, improper device positioning and scale pitch error can prevent realization of the full potential of the device.